Potentiometer



Aug. 18, 1959 J. E. GACH ErAL POTENTIOMETER Filed Nbv. 5, 1956 INVENTORS. JUNE E. GACH ROBERT L. GACH M, JM

A TTORNEVS United States Patent O POTENTIOMETER June E. Gach and Robert L. Gach, Claremont, Calif.,

assignors, by mesne assignments, to Daystrom, Incorporated, Elizabeth, N.J., a corporation of New Jersey Application November 5, 1956, Serial N 0. 620,474

2 Claims. (Cl. 338-149) The invention relates to potentiometers and more particularly to such devices responsive to rotational adjustment.

One conventional form of potentiometer has an elongated resistance element disposed in helical configuration in a case. Various means are employed to move an electrically conductive contact arm along the helix to obtain for example a linear response to the displacement of the contact along the resistance element. Conventional arrangements for displacing the contact arm result in problems such as backlash due to the spring loading of the contact against the resistance element. Also, the contact carrier tends to cant within the case and bind against further rotation. Usually these problems result because the conventional means for carrying the contact arm depends upon springing the means with respect to the case or resistance element to maintain the position of the contact carrying means. The invention solves the conventional problems by providing means for moving the contact arm that is not dependent upon contact with the resistance element to maintain the position of the contact arm with respect to the axis of rotation. The invention contemplates a potentiometer comprising a case and an elongated resistance element supported as a helix in the case. The case journals a control shaft rotatable within the helix. Means responsive to the rotation of the shaft guide a conductive contact arm along the length of the resistance element. Additional electrically conductive means are connected to the resistance element of the contact arm for access exteriorly of the case.

Preferably, the means responsive to the shaft rotation for guiding the contact arm comprises a disk that is slidable on the shaft and rotatably fixed with respect to the shaft. A portion of the disk periphery is notched and the contact arm is supported in the notch. The major portion of the disk periphery is helically threaded so that it matches and engages the helically disposed resistance element. This provides means for moving the contact arm along the length of the resistance element in response to rotation of the control shaft.

The contact need not reside in a notched portion in the disk. The disk may have a plurality of helical turns and the contact arm may reside within a turn. Alternately, a flexible wire or pigtail" contact may be used.

It is possible to support an elongated resistance element within the case so that the resistance element is disposed in a helix residing below the inner surface of the case. With such an arrangement the threaded portion of the disk carrying the contact arm may be guided by the portions of the case intermediate of each turn of the resistance element itself. The above element arrange-' ment could be achieved by plating with a conductive substance the root ofa thread form formed in the inner periphery of the case. However, the preferred form of the invention. utilizes a resistance element disposed to protrude from the inner surface of the case.

Patented Aug. 18, 1959 The contact arm, as stated above, is carried by the disk which is mounted to the shaft. The contact arm is thereby fixed radially with respect to the axis of rotation. Therefore, the spring loading force of the contact arm need only be sufficient to insure good electrical connection between the contact and the resistance element. The lesser spring loading possible of the invention adds to the longevity of the device. Radial restraint stemming from the disk being radially fixed with respect to the shaft results in a similar benefit with respect to the frictional contact of the disk with the resistance element. No loading of the disk against the resistance element is necessary and since the major portion of the disks periphery is in contact with the element, a lesser frictional load at each point of contact is required to obtain the necessary guiding of the disk by the element.

An objectionable feature in most conventional potentiometers is the sensitivity to vibration caused by the electrical connection between the contact arm and the means conductively connecting the contact arm to the exterior means for completing the circuitry of the potentiometer. In most devices the contact arm is in slidable contact with a portion of an elongated collector bar. The contact is disturbed by impact shock or rapid displacement of the potentiometer. The invention enables the contact arm to be slidably connected to the collector bar so that portions of the arm bear against opposite sides of the collector bar. Thus, displacement in any direction results in breaking of the arm to collector bar contact on only The end pieces which close the case are provided with stops projecting inwardly. The end pieces are adjustable Within the case so that the pin in the disk engages a stop in an end piece at each extreme of its travel along the shaft. The stop pins can be repositioned because the end pieces are adjustable and the potentiometer may be phased by positioning the pins to select the extreme points between which the contact arm travels on the resistance element.

The aforementioned and other advantages of the invention are explained in more detail with respect to the following specification and drawing, in which:

Fig. 1 is a sectional elevation of a preferred embodiment of the invention taken along the longitudinal axis of the control shaft;

Fig. 2 is an elevational view of the shaft and disk assembly;

Fig. 3 is a transverse sectional elevation taken along line 3-3 of Fig. 1;

Fig. 4 is a transverse sectional elevation taken along line 4-4 of Fig. 1;

Fig. 5 is a transverse sectional elevation taken along line 5-5 of Fig. 1;

Figs. 6 and 7 are fragmentary views of an additional embodiment of the contact means between the collector bar and the contact arm; and

Figs. 8 and 9 are fragmentary views of an additional means of contact between the collector bar and the contact arm.

The embodiment of the invention illustrated in Figs. 1 through 5 comprises a hollow case 10 having a cylindrical tube 11 and first and second end pieces 12 and 13. Each end piece has a reduced diameter portion 15 adapted to fit within the tube 11. The end pieces close the case and journal a control shaft 17 which extends through the first end piece 12 and the tube to the second end piece 13. An elongated resistance element 19 is disposed as a helix Within the tube of the case.

As illustrated in Fig. 1, the resistance element is partially embedded in the wall of the tube. The resistance element of the embodiment of Fig. 1 comprises a small resistance wire 20 wrapped about a base wire 21 of larger diameter that is disposed as a helix in the case.

Near each end of the helix formed by the wrapped base wire an end portion 23 of the resistance wire is conducted through a hole in the tube wall and fastened at an exterior terminal 24 mounted to the exterior wall of the tube.

The elongated resistance element of the potentiometer need not be of the type shown in Fig. 1. A simple conductive wire may be substituted for the wrapped Wire of Fig. 1. The choice of resistance elements will vary with the conductive capacity desired for a particular potentiometer use.

Control shaft 17 extends through end piece 12 and through the case to end piece 13. Its center of rotation coincides with the axis of the helix formed by the resistance element. An exterior portion 26 of the control shaft is cylindrical in configuration and is rotatably supported within an outwardly protruding boss 28 formed integrally with end piece 12. The boss has an exterior thread 29 for mounting the potentiometer to a panel. The end of the control shaft remote from the exterior portion is a stub 31 of substantially reduced diameter rotatably supported in a bore 32 extending through end piece 13.

A key portion 34 of the shaft is intermediate of the exterior portion and the stub. The key portion is substantially co-extensive with the longitudinal extent of the resistance element disposed in the case. The key portion mounts a'carrying disk 36 that is slidable on the key portion and restrained by the key portion from rotary or radial motion with respect to the key portion. As best illustrated in Fig. 3, the disk contains a central opening 38 conforming substantially to the cross sectional configuration of key portion 34 of the control shaft. The fit between the central opening and the key portion is such that the disk slides easily longitudinally of the shaft but is restrained as mentioned above from radial or rotary motion with respect to the shaft. The frictional contact between the central opening and the key portion may be reduced by arcuate indentations 39 in each wall of the opening.

The disk contains an indexing pin 41 extending beyond each face of the disk. A notch 43 in the outer periphery of the disk is located diametrally opposite the indexing pin. A contact arm 45 is supported in the notch by means of a U-shaped band 46 disposed about the arm and pinned at 47 to the disk.

The contact arm has the configuration of a V (see Fig. 3) in which one leg is a brush stem 48 contacting the resistance element and the other leg is a split stem 49 extending inwardly along one side of the notch.

A large insulated collar 51 is fixed to the control shaft between the key portion and end piece 12. A small insulated collar 52 is fixed to the shaft between the key portion and end piece 13. A collector bar 54 of conductive material is suspended parallel to the extent of the shaft between the two insulated collars. The collector bar is displaced from the shaft so that it extends through the notched portion of the disk. The split stem 49 is bifurcated to form a pair of fingers 55 one of which bears against each side of the collector bar.

The notch in the disk carrying the contact arm leaves the majority of the outer periphery of the disk. The remaining outer periphery has a helical thread 57 engaging that portion of the helically disposed resistance element protruding from the inner wall of the potentiometer case. The thread is so oriented on the periphery of the disk that the brush stern of the contact arm is in contact with a single turn of the resistance element. The orientation with respect to the contact arm is best seen in Fig. 2 which illustrates the assembly of the rotating parts of the potentiometer.

'Gontinuity between the point of the helically disposed resistance element touched by the contact arm and an external electrical contact 60 is by means of the collector bar and a continuity ring 61, a brush 62, and a stator ring 63. The continuity ring is fixed to insulated collar 52 and an arm 65 of the collector bar is bent down and electrically connected to the ring. The brush is a discontinuous ring of thin wire bonded to ring 61 at 67. Adjacent to the point of bonding the brush slants away from the continuity ring so that the disconnected ends of its circle are in contact with a face of the stator ring. The stator ring resides in an annular recess 68 in the inner face of end piece 13. The interiorly protruding portion of outer contact 60 passes through a slot 70 extending from the inner recess to the outer edge of the end piece.

The electrical path through the potentiometer is from an exterior post 24 through a portion of the resistance element to the point tapped by the contact arm, through both stems of the contact arm to the collector bar and from the collector bar to the continuity ring. Electrical flow is transferred from the revolving continuity ring to the stator ring 63 by means of brush 62 and thence to exterior contact 60.

Each end piece has a stop 72 protruding inwardly to the end piece. The stops are located with respect to the rotational center of the control shaft so that the indexing pin in the disk will strike a stop pin at each end of the travel of the disk. A hole 74 extends through large insulated collar 51 to permit the indexing pin to extend beyond the collar and strike the stop pin in end piece 12. Since the end pieces are rotatable with respect to the tube of the case and therefore with respect to the helically disposed resistance element, the starting and terminal positions of the contact arm with respect to the resistance element may be adjusted by movement of the end pieces.

Rotational displacement of the end pieces changes the location of the stops. The change in position of the stops will impede the further rotation of the disk and therefore the contact arm so that the contact arm taps the resistance at a changed point. This enables simple phase adjustment of the potentiometer of the invention. The end piece may be fixed in place by suitable means once the phasing has been accomplished. Figs. 6 and 7 illustrate a form of contact having a stem in which fingers 80, 81 are attached to a stem 82 instead of being an integral part of the contact arm stem. As best viewed in Fig. 6, finger is in contact with the upper surface of a collector bar 84 while finger 81 contacts the opposite surface of the collector bar. The ends of the fingers 80 and 81 are shaped to substantially match the configuration of the collector bar so that the area of contact is increased.

Figs. 8 and 9 illustrate a further embodiment of the split stem in which the stern of a contact arm 85 is trifurcated to form a pair of lower fingers 86 and an upper finger 87. Use of contact arms having configurations illustrated in Figs. 1 and 3 or 6 through 9 provides an electrical contact between the contact arm of the potentiometer and the collector bar that is insensitive to shock or sudden displacement of the potentiometer. In each of the embodiments a portion of the contact arm stem bears against an opposite side of the collector bar so that sudden motion in one direction can result in displacement of only one of the contact fingers from the collector bar.

In the operation of the illustrative potentiometer rotation of the control shaft results in rotation of the carrying disk and its associated contact arm. Since the threaded outer periphery of the disk is threadably engaged with the helically disposed resistance element, rotation will also impart a longitudinal motion of the disk and contact arm. The resultant of the rotary and longitudinal motions carries the contact arm along a helical path within the case duplicating the path in which the resistance element is disposed. Thus, the contact arm may be moved the entire length of the resistance element.

The contact arm is designed with sufficient spring loading to keep the brush stem of the contact arm in good electrical contact with the resistance element. The loading need only be sufficient to accomplish this purpose since no springing is necessary to float the disk carrying the contact arm within the helix due to its mode of attachment to the key portion of the shaft.

Many variations in shape are capable of supporting the disk on the key portion. While the illustrated embodiment shows the key portion as having a square cross section, this configuration may vary considerably, providing the central opening of the disk has a configuration permitting the disk to slide on the key portion and at the same time be restrained radially and rotationally with respect to the shaft. For instance, both the key portion and central opening may have triangular configurations, or the disk may have a rectangular notch in a circular opening to receive a key disposed longitudinally in the surface of a cylindrical key portion.

For practical purposes the resistance element has been illustrated as disposed in a spaced helix within the case, as this allows more bearing surface between the resistance element and the threaded portion of the disk periphery. The successive turns of the resistance element may be contiguous, however, if there is no need for the larger bearing surface between the resistance element and the disk as afforded when the turns of the helix are spaced from each other.

The configuration of the brush stem of the contact arm may also be varied to meet the dilfering conditions of contact imposed by different methods of disposing the resistance element in a helix within the case of the potentiometer.

We claim:

1. A potentiometer, comprising: a case, an elongated resistance element supported as a space wound helix in the case, a shaft journalled for rotation in the case within the helix, a disk rotatable with said shaft and slidably keyed on the shaft for axial movement thereon, said disk having a peripheral circumferentially extending opening therein, the periphery of the disk being threaded to engage at least one turn of the helix in a portion thereof extending from opposite sides of said opening, a spring contact mounted on the disk in said opening engageable with the resistance element in the portion of said helix turn adjacent said opening as the disk travels along the helix, a collector bar supported at its opposite ends on said shaft, said bar being positioned radially outwardly from and parallel to the shaft axis, and extending through said disk opening, means slidably connecting the contact to the collector bar, and electrically conductive means connected to the resistance element and the collector bar for access exteriorly of the case.

2. A potentiometer according to claim 1, in which the contact comprises a longitudinally V-shaped strip of conducting material anchored between its ends in the peripheral opening of the disk, one leg of said contact being positioned to engage the resistance element, and the other leg thereof being split to provide finger portions for contacting the collector bar on opposite sides thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,152,913 Sagle Sept. 7, 1915 1,561,137 Burns Nov. 10, 1925 2,361,010 Cary et a1 Oct. 24, 1944 2,371,159 Erb Mar. 13, 1945 2,454,986 Beckman Nov. 30, 1948 2,473,048 Beckman June 14, 1949 2,558,326 Van Dyke June 26, 1951 2,595,189 Dewan Apr. 29, 1952 2,813,956 Sorber Nov. 19, 1957 

